Contact structure for mechanical rectifiers



o. JENSEN 2,853,552

CONTACT STRUCTURE FOR MECHANICAL RECTIFIERS Sept W58 .4 Sheets-Sheet 1 Filed Jan. 10, 1956 m R V% m m W V w A a 7 W M 0. JENSEN ept. 9, i958 CONTACT STRUCTURE FOR MECHANICAL RECTIFIERS Filed Jan. 10, 1956 v 4 Sheets-Sheet 2 INVENTOR. i770 JE/YJE/V Sept. 9, 1958 o. JENSEN 2,851,562

CONTACT STRUCTURE FOR MECHANICAL RECTIFIERS Filed Jan. 10. 1956 4 Sheets-Sheet 3 BY W,

,4 770,9 N ZS Sept. 9, 1958 o. JENSEN 2,851,552

CONTACT STRUCTURE FOR MECHANICAL RECTIFIERS FiledJan. 10, less 4 Sheets-Sheet 4 CONTACT STRUCTURE F011 MECHANICAL RECTIFIERS Otto Jensen, Malvern, Pa., assignor to li=T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application January 10, 1956, Serial No. 558,350

16 Claims. (Cl. 200-166) My invention relates to a contact structure for mechanical rectifiers and more specifically to a contact structure in which the fixed contacts which cooperate with a movable bridging contact are provided with at least four contact surfaces which may be used individually.

Electrical contacts which are constructed to be used in conjunction with a mechanical rectifier may be seen with reference to my copending application, Serial No. 307,- 067, filed August 29, 1952. The type of contact shown therein comprises a pair of stationary contacts and a cooperating movable contact which is biased into engagement with the above mentioned pair of stationary contacts. One of the stationary contacts is then connected to a D.-C. conductor or bus, and the other stationary contact is connected to an A.-C. conductor or bus.

Rectification is then achieved by driving the movable contact into and out of engagement with the stationary contacts to thereby connect the A.-C. conductor to the D.-C. conductor or to disconnect the two conductors by means of a mechanical or electromagnetic system.

If now an A.-C. source of power is connected in series with the A.-C. conductor, D.-C. conductor, contact structure and a D.-C. conductor load, then by opening the contact when the potential of the A.-C. source is negative and closing the contact when the potential of the A.-C. source is positive, an average potential will be impressed.

In order to assure that an extremely small current is being carried by the contact at the time of contact opening and closing, a commutating reactor which is clear- 1y described in my copending application, Serial No. 301,- 880, filed July 31, 1952,, may be connected in series with the contact.

It is to be understood, however, that since the contacts of a mechanical rectifier will operate 216,000 timers per hour when rectifying a 60 cyclesource, that despite all protective means that a certain amount of contact wear will occur and that after a certain length of time that the contact surfaces will have to be refinished or the contacts will have to be replaced.

In the case of the previously used contact structures described above in my copending application, Serial No. 307,067, the stationary contacts provide only one available contact surface for cooperation with the movable contact. Hence, wear on this contact surface necessitated removal of the complete contact structure whereupon this structure is disassembled and, if possible, the contact surface is refinished and thereafter replaced in the mechanical rectifier unit.

The principle of my invention is to overcome this disadvantage by providing a stationary contact which may be of a substantially square shape wherein the surface beginning at either of the four edges may be utilized as a contact surface to cooperate with the movable contacts. Hence, it is apparent that when one of the available surfaces has been subjected to a prohibitive amount of wear in its cooperation with the movable contact that the fixed contact in question need only be rotated by 90 degrees whereupon a fresh contact surface will be provided.

2,851,562 Patented Sept. 9, 1958 In this manner, it is seen that one surface of the fixed contact will provide at least four contact surfaces and, if desired, by turning the fixed contact over to present its opposite surface that still another four contact surfaces are available. Hence, one substantially square block of current carrying material suitable for contact purposes for mechanical rectifiers can now be made in such a manner as to provide eight contact surfaces for a fixed contact.

It is seen that these substantially square contacts described above will have a greater mass than the fixed contacts of previously used contact structures. This, however, offers several advantages; the most important being that better heat and current transfer to the connecting bus bars is afforded.

Accordingly, a primary object of my invention is to provide a contact structure for mechanical rectifiers in which each of the fixed contacts may provide more than one available contact surface for cooperation with the movable contact.

Another object of my invention is to provide a fixed contact for mechanical rectifier contact structures wherein the fixed contact is of substantially square shape, and the surfaces adjacent to the four edges of the contact are individually available for cooperation with a movable contact.

Another object of my invention is to provide a contact structure for mechanical rectifiers wherein the contact structure need not be replaced due to wear of one of the fixed contact surfaces.

Another object of my invention is to provide a fixed contact structure for mechanical rectifier contacts in which a plurality of contact surfaces are available for cooperation with the movable contact, and the contact mass is increased to afford better heat and current conduction to the bus bar connected to the stationary contact in question.

Since the available time for complete contact engagement or disengagement is substantially limited to the length of time of the commutating reactor step which may be of the order of a fraction of a milli-second, it is essential that contact engagement takes place with substantially no bounce. Previously used contact structures for mechanical rectifiers have utilized a substantially homogeneous contact for a contact which is solid silver throughout. I propose to use a contact having a copper core and a facing of contact material which may be a silver compound such as that known by the trade name Gibsalloy. It is therefore seen that my novel contact will in effect he a sandwich when the relatively soft copper core will absorb shock and prevent bouncing.

Accordingly, another object of my invention is to provide a fixed contact for mechanical rectifier contact structures which is comprised of a copper core and a contact surface which is a facing on the contact core comprised of a silver compound which is of relatively hard material.

Another object of my invention is to prevent contact bounce by utilizing stationary contacts having a core of substantially softer material than the material of the contact surfaces.

During contact operation the vibration of the contacts is in the order of 800 to 1200 cycles per second and has irregular velocity and acceleration with a maximum amplitude in the order of 0.004 inch.

This movement of the stationary structure is in a horizontal, vertical and longitudinal direction of non-periodic oscillation with each of the bus 'bars vibrating independently. Hence, although a guide means can hold and maintain the bridging contact against rotation and sliding or tilting it is impossible to provide complete guiding for a bridging contact which engages bus bars that have the above mentioned independent non-periodic irregular oscillation.

Difficulty arises at two points within the cycle of operation, namely when the bridging contact initially engages and when it disengages the stationary contacts. Since the frequency of contact engagement and disengagement is different from the frequency of stationary structure there are two instances within every cycle of operation where the motions of the cooperation components may be in the same or opposite direction.

This of course, will result in undue friction or galling and wearing off of tiny silver particles from the cooperating surfaces which will rapidly oxidize the silver dust. The current flow during the contact engaged portion of the cycle will gradually weld these dust particles to one of the cooperating contacts depending on the direction of current flow. The contact creation of silver dust and the constant welding of the silver dust results in the nudesirable transfer of material on the cooperating contacts.

It is possible to partially eliminate this undesirable effect by providing a lubricating material between the cooperating contact surfaces to convert the undesirable friction into sliding motion.

By way of example, one such contact material which offers the above noted characteristics consists of 97 /2% sintered silver and 2 /2% cadmium oxide. The cadmium oxide reduces the sticking of the cooperating contacts which previously occurred by welding and hence, substantially reduces material transfer.

Accordingly another object of my invention is to provide a lubricating material for the contact surfaces of a mechanical rectifier contact surface.

Another object of my invention is to utilize a sintered silver contact containing cadmium oxide therein for the contact surfaces of a mechanical rectifier contact.

As was previously described, the movable contact is biased to he in engagement with the stationary contacts and may operate out of engagement by means of a mechanical push rod structure. This biasing means has been a helical spring under compression wherein one end of the helical spring is fixed and the other end carries the movable contact. In view of this type construction, it is to realized that upon compression and ex tension of the spring that the free end or the end which carries the movable contact will undergo an angular rotation. It has been found, that this rotary motion with its associated high forces is extremely detrimental to the operation of the contact structure in that it causes a loosening effect between the guide member and the contact itself when contact guiding is effected in a manner shown in copending application, Serial No. 438,465, filed June 22, 1955.

I now propose a method which will defeat this rotary motion comprising the use of two springs for biasing the movable contact into engagement with the cooperating stationary contacts. More specifically, I provide two concentric springs, one wound in a right hand direction and the other wound in a left hand direction. It is therefore seen that upon extension for compression of the concentric springs of my invention that they will tend to rotate the free end carrying the contact structure in opposite directions and thereby cancel the net rotation of the movable contact. Although this will cause additional stresses to appear in the spring wire, judicious design of the springs will prevent failure thereof due to the stresses, and relation motion between the movable contact and its guide members will be defeated.

Accordingly, another object of my invention is to provide means for defeating the relative motion between the movable contact and its guide members.

Another object of my invention is to provide a biasing means. for the movable contact of a mechanical rectifier contact structure which is so constructed as to prohibit rotation of the movable contact during its motion into and out of engagement with the cooperating stationary contacts.

Another object of my invention is to provide a biasing means for biasing the movable contact of a mechanical rectifier contact structure into engagement with its cooperating stationary contact which is comprised of a pair of concentric springs, one being wound in a left hand direction and the other being wound in a right hand direction, whereby axial rotation of the springs due to extension and compression thereof is substantially cancelled.

Effective guiding of the movable contact has been shown to be essential to the above mentioned copending application, Serial No. 438,465. An essential limitation that must be met by a guide means for the movable contact is that proper provision must be made for preventing stress concentration at the deflection points of the guide. I therefore propose the use of a novel guide member in which the deflection arms of the guide are relatively long to thereby equalize the stress along the guide member arm.

By designing this novel guide in such a manner as to have it replaceable by an equivalent spring diagram which is comprised of four support wires for members which are at right angles to one another, it is seen that my novel guide member will prevent both a skew motion of the movable contact or a motion of the contact which is in a plane different from the normal plane of the contact and to also prevent a rotary motion of the contact about its own axis.

Therefore, another object of my invention is to provide a spring guide for a mechanical rectifier contact which is substantially comprised of four mutually perpendicular support arms which are fastened to the movable contact and have relatively long flexing arms to thereby distribute stresses in the best possible manner.

These and other objects of my invention will become apparent when taken in conjunction with the following drawings in which:

Figure 1 is a schematic electrical connection diagram of a mechanical rectifier to which my invention may be applied.

Figure 2 is a perspective view of an operating mechanism for operating the movable contact of a mechanical rectifier contact structure into and out of engagement.

Figure 3 is an exploded perspective view of the contact structure of my invention.

Figure 4 is a side cross-sectional view of the contact structure shown in Figure 3 wherein the stationary contacts are connected to their respective electrical conductors or buses.

Figure 5 is a top cross sectional view when taken across the line 55 of Figure 4.

Figure 6 is similar to Figure 4 and'has been modified to show concentric springs used as the biasing means for the movable contact and goes furtherto show the stationary contacts as having a sandwich-type construction.

Figure 7 shows a top view of the stationary contacts of my invention wherein each stationary contact has one surface available for cooperation with the movable contact and the other surfaces which are not in use are covered by aprotective material to prevent damage thereof.

In Figure 1, an AC. voltage source which is not shown energizes the conductors 10 which in turn energize the circuit breaker s'een schematically at 11 and finally the primary winding of the transformer 12. The current is subsequently passed from the secondary windings of the transformer 12 to the commutating reactors 13 which stop the current as set forth in U. S. Patent 2,693,569.

The current then passes throughthe disconnect switches 14 to the contact assemblies shown only for phase A as contacts 15 and 16. Contact assemblies 15 and 16' are sequentially operated in synchronism with the frequency of the A.-C. source and'thereby connect the alternating source buses a, 10b and 100 to the direct current or load buses 20 and 21 in a predetermined manner.

For purposes of simplification, I have shown in Figure 2 the mechanical switching arrangement which is utilized only for phase a of Figure 1, it being understood that the switching apparatus for phases b and c are identical in construction.

A synchronous motor 30 drives the shaft 31 which in turn operates the eccentric member 32 to thereby alternately drive the push rods 33 and 34 upwardly through the bell crank 35. A detailed explanation of the construction of the adjustment and control by the means 36 as well as a more complete description of the operating mechanism per se is set forth in previously mentioned copending application, Serial No. 397,367.

The upward movement of the push rod 34 will urge the movable contact 37 upward against the bias of the helical spring 38 and thereby disengage it from engagement with the stationary A.-C. contact 28 and the stationary D.-C. contact 26, these two contacts being in engagement with the 'A.-C. bus 10a and D.-C. bus 20 respectively. A more complete description of the contact structure which is the subject of the instant invention will be given hereinafter.

During the period of time in which the movable contact 36 is maintained in the disengaged position by the push rod 34, it is seen that the push rod 33 is in a disengaged position with respect to its associated movable contact 39 of the contact structure 16, and hence, the contact 39 will be in contact engagement with the stationary contacts 40 and 41 respectively to thereby form a connection between the A.-C. bus 10a and the D.-C. bus 21.

During the next half cycle, however, the position of the push rods 33 and 34 will be reversed by the bell crank 35, and it is the push rod 33 that will operate to disengage the movable contact 39 and its cooperating stationary contacts 40 and 41. Similarly, the movable contact 37 of the contact structure will have been moved into engagement with the stationary contacts 26 and 28 to thereby connect the A.-C. bus 10a to the D.-C. bus bar by virtue of the biasing spring 38.

Thus, throughout a complete cycle of operation, the bridging contacts will complete a mechanical cycle of operation, and an average D.-C. potential will be connected across the D.-C. bus bars 20 and 21.

The specific structure of the contacts 15 and 16 may now be seen with reference to Figures 3, 4 and 5. In each of these figures, the stationary contacts are shown as contacts 50 and 51 respectively. As may be seen in either of Figures 3 or 4, contacts 50 and 51 are pivotally mounted at their center by means of center bolts 52 and 53 respectively. The center bolts 52 and 53 are more specifically constructed to have an upwardly protruding portion 54 and 55 respectively which are constructed to subsequently engage the nut posts 56 and 57 respectively, and each of the center bolts 52 and 53 have a downwardly protruding portion 58 and 59 respectively. Each portion 58 and 59 of the center bolts 52 and 53 respectively is then constructed to be fastenable to a current carrying bus. This is clearly seen in Figure 4 in which the portion 58 of the center bolt 52 is shown as being screwed into the D.-C. bus 60 whereby high contact pressure will be exerted by a means which will be described hereinafter to secure the fixed contact 50 to the bus 60.

It is to be noted that the bus 60 may be the D.-C. bus of the system utilizing the contact structure of Figures 3 and 4 and that the bus 61 of Figure 4 may be the A.-C. bus of the rectifier system. Clearly, the center post 53 having the protruding portion 59 will be utilized in fastening the stationary contact 51 to the A.-C. bus 61 in the same manner as was the stationary contact 50 fastened to the D.-C. bus 60.

Steel pressure blocks 62 and 63 are shown in each of Figures 3 and 4 as being applied directly on top of the stationary contact 50 and 51 respectively, these pressure blocks being coaxial with the center bolts 52 and 53 respectively. It is by means of the pressure block 62 and 63 that the stationary contacts 50 and 51 respectively are maintained in rigid current carrying relationship with their respective current carrying buses and 61. This may be seen in each of Figures 3 and 4 wherein the steel pressure blocks 62 and 63 are clamped down when the nut posts 56 and 57 are secured to the upwardly extending portions 54 and S5 of the nut posts 52 and 53 respectively. By providing this construction, it is seen that the nut pressure is distributed over a larger area to thereby assure distributed contact pressure over the interface between the fixed contact and their associated buses.

A movable contact 64 is then positioned to be brought into bridging engagement or disengagement with respect to the stationary contacts 50 and 51 as seen in each of Figures 3, 4 and 5. The movable contact 64 is more specifically secured to a guide member 65 by means of the spring pad 66 and the screw means 67 which 00- operates with an internal thread 68 in the movable contact 64.

The spring 65 which may be of a material such as melamine is then secure to the pressure blocks 62 and 63 by means of the screw means 69a and 69 respectively. It is now clear that the movable contact 64 which is supported at the center of the melamine guide 65 which in turn is fixed to the pressure blocks 62 and 63 is movable along its perpendicular axis to be moved into and out of engagement with one surface of the stationary contact 58 and another surface of a stationary contact 51.

A biasing means which in the case of Figures 4 and 5 is the spring 70 is provided to maintain the movable contact 64 in engagement with the stationary contacts 50 and 51. More specifically, this helical spring 70 is connected at one end to the spring pad 66 and is connected at the other end to a spring pad 71 which in turn is supported from the contact block 72 by means of the bolt 73. Bolt 73 may then be further utilized to adjust contact pressure between the movable contact 64 and the stationary contacts 50 and 51.

The contact block 72 is seen in Figure 3 as comprising a first slot 74 and a second slot 75, these slots being arranged to receive the necks 76 and 77 of the nut posts 56 and 57 respectively.

It is now apparent that in assembling the contact structure seen in Figures 3, 4 and 5 that one need only place the components in their relative positions with respect to one another and to thereafter insert the contact block 72 and tighten the nut posts 56 and 57 which will thereby fix the pressure blocks 62 and 63 respectively to maintain the contacts 50 and 51 in rigid connection with their associated buses and further serve to maintain the helical spring 70 in position by virtue of the fastening of spring pad 71. Similarly, in fastening the pressure blocks 62 and 63, it is seen that the melamine guide 65 and hence, the movable contact 64, will be definitely and rigidly positioned for subsequent operation of the movable contact 64 with respect to the stationary cooperating contacts 50 and 51.

The essence of my novel invention may now be understood with reference to Figures 3 and 4. That is, because of the construction of the fixed contacts 50 and 51 and their mounting on the central center bolts 52 and 53 respectively, by loosening the nut posts 56 and 57 that the contacts 5t) and 51 may be rotated to present a new contact surface to the movable contact 64.

Therefore, if in the course of operation, the contact surface of the stationary contacts 50 and 51 is worn or damaged to a prohibitive degree, one merely needs to loosen the nut posts 56 and 57 without disassembling the complete contact structure and to then rotate the fixed contacts about their pivotal points 52 and 53 to present a new and undamaged contact surface. Clearly, four contact surfaces are available on one side of either contact t and51. If after using each of these four surfaces still another contact surface is required, it is seen that the contact assembly may be disassembled only to the degree required to allow reversing the contacts 59 and 51 to thereby present four new and clean available contact surfaces.

The spring guide 65 which is seen in Figures 3 and 4 may be more specifically described in conjunction with the top view of Figure 5. Reference to Figure 5 makes it obvious that the deflection of the spring 65 will take place approximately along the lines 78 and 79 which are defined by the slots 89, 81 and 82 and 83 respectively. This construction, in effect, provides four supporting arms for the movable contact 64 which are relatively long to thereby substantially distribute the stress at points 68 and 69 over a long distance. Similarly, the construction is a rugged one which would prevent rotation of the contact 64 about its axis as well as a skew motion or a change in the plane of the contact 64.

Figure 6 which is similar to Figure 4 in that it shows a side cross sectional view of the assembled contact structure of Figure 3 differs therefrom in the construction of the biasing spring which biases the movable contact 64 into engagement with the cooperating stationary contact and in the construction of the stationary contact itself. It is seen in Figure 6 that each of the stationary contacts shown generally at 5'9 and 51 are more specifically comprised of a copper core 84 and 85 respectively which is sandwiched between a relatively hard contact material surface 86, 87, 88 and 89 respectively. The surfaces 86, 87, 88 and 89 may, if desired, be of a silver compound which is relatively hard and of relatively high current conductivity. This function will serve the purpose of absorbing the shock created upon engagement of the movable contact 64 and the stationary contacts 50 and 51 since the relatively soft copper center 84 and 85 will flex to absorb the energy of impact.

The'contact surfaces 86 and 89 of Figure 6 may if desired be made of a material having lubricating quantities such as a sintered silver material having a relatively small amount of cadmium oxide therein to thereby decrease the galling action between the cooperating contacts. In a like manner, it is to be realized that the contacts seen in Figures 3 through 5 may also be constructed of a lubricating material.

Figure 6 further shows the use of two concentric springs 90 and 91 for fastening the movable contact 64 to the contact housing 72. One of the springs is wound in a right hand direction and the other of the springs is wound in a left hand direction. Therefore, upon extension or contraction of the springs, it is seen that their angular rotations will be equal and opposite, and there will be no relative rotation between the movable contact 64 and its guiding spring 65. Because of this, additional stress will not be introduced into the guide member 65 due to the relative rotation.

Figure 7 shows a top view of the stationary contacts 50 and 51 and the movable contact 64. Here it is seen that only the surfaces indicated generally at 92 and 93 of contacts 50 and 51 cooperate with the movable contact 64, and the other surfaces are idle. It is desirable to protect these surfaces from contamination, and I have found that this can be done by providing an overlapping tape means shown as the tapes 94, 95, 96 in conjunction with the contact 59 and the tapes 97, 98 and 99 in conjunction with contact 51. If desired, instead of using the tape means shown in Figure 7, a spray which would harden to form a peelable protective layer could be utilized.

In the foregoing, I have described my invention solely in connection with specific illustrative embodiments thereof. Since many variations and modifications of the invention will now be obvious to those skilled in the art,

8 I prefer to be bound not by the specific disclosure herein contained but only by the appended claims.

I claim:

l. A contact structure for mechanical rectifier; said contact structure comprising a pair of stationary contacts, a movable contact and a biasing means; said movable contact being constructed to be movable into and out of bridging engagement with said stationary contacts; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; fastening means for normally rigidly maintaining each of said pair of stationary contacts in a predetermined position; each of said pair of stationary contacts being pivotally mounted whereby rotation of each of said pair of stationary contacts about said pivotal mounting presents at least a partially new contact surface for cooperation with the contact surface of said movable contact; the axis of rotation of said pivotally mounted stationary contacts being perpendicular to their contact surfaces. 7

2. A contact structure for mechanical rectifier; said contact structure comprising a pair of stationary contacts, a movable contact and a biasing means; said movable contact being constructed to be movable into and out of bridging engagement with said stationary contacts; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; each of said pair of stationary contacts having a substantially square shape; fastening means for normally rigidly maintaining each of said pair of stationary contacts in a predetermined position; each of said pair of stationary contacts being pivotally mounted at the center thereof whereby the four contact surfaces defined by the four edges of said substantially square stationary contacts are positionable for individual contact engagement with a contact surface of said movable contact; the axis of rotation of said pivotally mounted stationary contacts be ing perpendicular to their contact surfaces.

3. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts, a guide means, a movable contact and a housing means; each of said pair of stationary contacts and guide means being supported with respect to one another by said guide means; said movable contact means being connected to said guide means whereby motion of said movable contact is guided by said guide means; said guide means being positioned and constructed whereby said movable contact is movable into and out of bridging contact engagement with said pair of stationary contacts; a biasing means; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; an operating means; said operating means being constructed to operate said movable contact to a disengaged position against the action of said biasing means; fastening means for normally rigidly maintaining each of said pair of stationary contacts in a predetermined position; each of said pair of stationary contacts being pivotally mounted whereby rotation of each of said pair of stationary contacts about said pivotal mounting presents at least a partially new contact surface for cooperation with the contact surface of said movable contact 4. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts, a guide means, a movable contact and a housing means; each of said pair of stationary contacts and guide means being supported with respect to one another by said guide means; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said guide means being positioned and constructed whereby said movable contact is movable into and out of bridging contact engagement with said pair of stationary contacts; a biasing means; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; an operating means; said operating means heing constructed to operate said movable contact to a disengaged position against the action of said biasing means; each of said pair of stationary contacts having a substantially square shape; fastening means for normally rigidly maintaining each of said pair of stationary contacts in a predetermined position; each of said pair of stationary contacts being pivotally mounted at the center thereof whereby the four contact surfaces defined by the four edges of said substantially square stationary contacts are positionable for individual contact engagement with a contact surface of said movable contact.

5. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts, a guide means, a movable contact and a housing means; said movable contact means being connected to said guide means whereby motion of said movable con-- tact is guided by said guide means; said guide means being positioned and constructed whereby said movable contact is movable into and out of bridging contact engagement with said pair of stationary contacts; a biasing means; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; an operating means; said operating means being constructed to operate said movable contact to a disengaged position against the action of said biasing means; each of said pair of stationary contacts being pivotally mounted whereby rotation of each of said pair of stationary contacts about said pivotal mounting presents at least a partially new contact surface for cooperation with the contact surface of said movable contact; said biasing means comprising a first and second concentric helical spring; said first helical spring being Wound in a right hand direction; said second helical spring being wound in a left hand direction.

6. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts and a guide means and a movable contact; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said guide means being positioned and constructed whereby said movable contact is movable into and out of bridging contact engagement with said pair of stationary contacts; each of said pair of stationary contacts being pivotally mounted whereby rotation of each of said pair of stationary contacts about said pivotal mounting presents at least a partially new contact surface for cooperation with the contact surface of said movable contact; an operating means; said operating means being constructed to operate said movable contact into and out of engagement with said stationary contacts; a biasing means; said biasing means comprising a first and second concentric helical spring; said first helical spring being wound in a right hand direction; said second helical spring being wound in a left hand direction; the angular rotation imparted to said movable contact by said first and second helical springs during extension and compression thereof being of substantially equal magnitude and in opposite directions whereby relative motion between said movable contact and said guide means is avoided.

7. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts, a guide means, a movable contact and a housing means; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said guide means beingpositioned and constructed whereby said movable contact is movable into and out of bridging contact engagement with said pair of stationary contacts; a biasing means; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; an operating means; said operating means being constructed to op erate said movable contact to a disengaged position against the action of said biasing means; each of said pair of stationary contacts having a substantially square shape; each of said pair of stationary contacts being pivotally mounted at the center thereof whereby the four contact surfaces defined by the four edges of said substantially square stationary contacts are positionable for individual contact engagement with a contact surface of said movable contact; said biasing means comprising a first and second concentric helical spring; said first helical spring being wound in a right hand direction; said second helical spring being wound in a left hand direction; the angular rotation imparted to said movable contact by said first and second helical springs during extension and compression thereof being of substantially equal magnitude and in opposite directions whereby relative motion between said movable contact and said guide means is avoided.

8. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts, a movable contact and a biasing means; said movable contact being constructed to be movable into and out of bridging engagement with said stationary contacts; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; each of said pair of stationary contacts having a substantially square shape; fastening means for normally rigidly maintaining each of said pair of stationary contacts in a predetermined position; each of said pair of stationary contacts being pivotally mounted at the center thereof where by the four contact surfaces defined by the four edges of said substantially square stationary contacts are positionable for individual contact engagement withva contact surface of said movable contact; each of said stationary contacts being constructed to comprise a core of relatively soft current carrying material and a contact surface of relatively hard current carrying material whereby said core of relatively soft current carrying material is eifective to absorb shock during contact engagement to thereby limit contact bounce.

9. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts, a guide means, a movable contact and a housing means;

said movable contact means being connected to said guide pair of stationary contacts; a biasing means; said biasing means being constructed to bias said movable contact into engagement with said stationary contacts; an operating means; said operating means being constructed to operate said movable contact to a disengaged position against the action of said biasing means; each of said pair of station ary contacts being pivotally mounted whereby rotation of each of said pair of stationary contacts about said pivotal mounting presents at least a partially new contact surface for cooperation with the contact surface of said movable contact; said biasing means comprising a first and second concentric helical spring; said first helical spring being wound in a right hand direction; said second helical spring being wound in a left hand direction; each of said stationary contacts being constructed to comprise a core of relatively soft current carrying material and a contact surface of relatively hard current carrying material whereby said core of relatively soft current carrying material is effective to absorb shock during contact engagement to thereby limit contact bounce.

10. A contact structure for connecting and disc0nnecting a first and second bus bar; said contact structure comprising a first and second stationary contact and a movable bridging contact; a biasing means, a guide means, a center bolt, a nut post and a pressure block for each of said first and second stationary contacts; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said movable contact being movable into and out of bridging contact engagement with said first and second stationary contacts; said biasing means being constructed to bias said movable contact into bridging engagement with said stationary contacts; each of said first and second stationary contacts being positioned between their respective pressure blocks and buses; each combination of said pressure blocks and adjacent stationary contacts having its said center bolt extending therethrough; each of said center bolts being constructed to be fastenable at one end thereof to the bus bar corresponding to its stationary contact and to be fastenable at its other end to said nut post corresponding to its stationary contacts; each pair of said. center bolts and nut posts being constructed to be threadibly engaged; tightening of said threaded engagement being effective to impinge a portion of said nut post on said pressure block to thereby drive said stationary contact into engagement with its corresponding bus bar; each of said stationary contacts being rotatable about their said center bolts when said threaded engagement between their corresponding center bolts and nut posts is loosened to thereby present at least a partially new contact surface to said movable contact.

11. A contact structure for connecting and disconnecting a first and second bus bar; said contact structure comprising a first and second stationary contact and a movable bridging contact; a biasing means, a guide means, a center bolt, a nut post and a pressure block for each of said first and second stationary contacts; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said movable contact be ing movable into and out of bridging contact engagement wtih said first and second stationary contacts; said biasing means being constructed to bias said movable contact into bridging engagement with said stationary contacts; each of said first and second stationary contacts being positioned between their respective pressure block buses; each combination of said pressure blocks and adjacent stationary contacts having its said center bolt extending therethrough; each of said center bolts being constructed to be fastenable at one end thereof to the bus bar corresponding to its stationary contact and to be fastenable at its other end to said nut post corresponding to its stationary contact; each pair of said center bolts and nut posts being constructed to be threadibly engaged; tightening of said threaded engagement being effective to impinge a portion of said nut post on said pressure block to thereby drive said stationary contact into engagement with its corresponding bus bar; each of said pair of stationary contacts having a substantially square shape; each of said stationary contacts being rotatable about their said center bolts when said threaded engagement between their corresponding center bolts and nut posts is loosened whereby the four edges of said substantially square stationary contacts are positionable for individual contact engagement with a contact surface of said movable contact.

12. A contact structure for connecting and disconnecting a first and second bus bar; said contact structure comprising a first and second stationary contact and a movable bridging contact; a biasing means, a guide means, a center bolt, a nut post and a pressure block for each of said first and second stationary contacts; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said movable contact being movable into and out of bridging contact engagement with said first and second stationary contacts; said biasing means being constructed to bias said movale contact into bridging engagement with said stationary contacts; each of said first and second stationary contacts being positioned between their respective pressure blocks and buses; each combination of said pressure blocks and adjacent stationary contacts having its said bolt extending therethrough; each of said center bolts being constructed to be fastenable at one end thereof to the bus bar corresponding to its stationary contact and to be fastenable at its other end to said nut post corresponding to its stationary contact; each pair of said center bolts and nut posts being constructed to be threadibly engaged; tightening of said threaded engagement being eifective to impinge a portion of said nut post on said pressure block to thereby drive said stationary contact into engagement with its corresponding bus bar; each of said stationary contacts being rotatable about their said center bolts when said threaded engagement between their corresponding center bolts and nut posts is loosened to thereby present at least a partially new contact surface to said movable contact; said biasing means comprising a first and second concentric helical spring; said first helical spring being wound in a right hand direction; said second helical spring being wound in a left hand direction.

13. A contact structure for connecting and disconnecting a first and second bus bar; said contact structure comprising a first and second stationary contact and a movable bridging contact; a biasing means, a guide means, a center bolt, a nut post and a pressure block for each of said first and second stationary contacts; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said movable contact being movable into and out of bridging contact engagement with said first and second stationary contacts; said biasing means being constructed to bias said movable contact into bridging engagement with said stationary contacts; each of said first and second stationary contacts being positioned between their respective pressure blocks and buses; each combination of said pressure blocks and adjacent stationary contacts hav ing its said center bolt extending therethrough; each of said center bolts being constructed to be fastenable at one end thereof to the bus bar corresponding to its stationary contact and to be fastenable at its other end to said nut post corresponding to its stationary contact; each pair of said center bolts and nut posts being constructed to be threadibly engaged; tightening of said threaded engagement being eflfective to impinge a portion of said nut post on said pressure block to thereby drive said stationary contact into engagement with its corresponding bus bar; each of said pair of stationary contacts having a substantially square shape; each of said stationary contacts being rotatable about their said center bolts when said threaded engagement between their corresponding center bolts and nut posts is loosened whereby the four contact surfaces defined by the four edges of said substantially square stationary contacts are positionable for individual contact engagement with a contact surface of said movable contact; said biasing means comprising a first and second concentric helical spring; said first helical spring being wound in a right hand direction, said second helical spring being wound in a left hand direction; the angular rotation imparted to said movable contact by said first and second helical springs during extension and compression thereof being of substantially equal magnitude, and in an opposite direction whereby relative motion between said movable contact and said guide means is avoided.

14. A contact structure for connecting and disconnecting a first and second bus bar; said contact structure comprising a first and second stationary contact and a movable bridging contact; a biasing means, a guide means, a center bolt, a nut post and a pressure block for each of said first and second stationary contacts; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said'guide means; said movable contact being movable into and out of bridging contact engagement with said first and second stationary contacts; said biasing means being constructed to bias said movable contact into bridging engagement with said stationary contacts; each of said first and second stationary contacts being positioned between their respective pressure blocks and buses; each combination of said pressure blocks and adjacent stationary contacts having its said center bolt extending therethrough; each of said center bolts being constructed to be fastenable at one end thereof to the bus bar corresponding to its stationary contact and to be fastenable at its other end to said nut post corresponding to its stationary contact; each pair of said center bolts and nut posts being constructed to be threadibly engaged; tightening of said threaded engagement being effective to impinge a portion of said nut post on said pressure block to thereby drive said stationary contact into engagement with its corresponding bus bar; each of said stationary contacts being rotatable about their said center bolts when said threaded engagement between their corresponding center bolts and nut posts is loosened to thereby present at least a partially new contact surface to said movable contact; each of said stationary contacts being constructed to comprise a core of relatively soft current carrying material and a contact surface of relatively hard current carrying material whereby said core of relatively soft current carrying material is effective to absorb shock during contact engagement to thereby limit contact bounce.

15. A contact structure for connecting and disconnecting a first and second bus bar; said contact structure comprising a first and second stationary contact and a movable bridging contact; a biasing means, a guide means, a center bolt, a nut post and a pressure block for each of said first and second stationary contacts; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said movable contact being movable into and out of bridging contact engagement with said first and second stationary contacts; said biasing means being constructed to bias said movable contact into bridging engagement with said stationary contacts; each of said first and second stationary contacts being positioned between their respective pressure blocks and buses; each combination of said pressure blocks and adjacent stationary contacts having its said center bolts extending therethrough; each of said center bolts being constructed to be fastenable at one end thereof to the bus bar corresponding to its stationary contact and to be fastenable at its other end to said nut post corresponding to its stationary contact;

14 each pair of said center bolts and nut posts being con structed to be threadibly engaged; tightening of said threaded engagement being elfective to impinge a portion of said nut post on said pressure block to thereby drive said stationary contact into engagement with its corresponding bus bar; each of said stationary contacts being rotatable about their said center bolts when said threaded engagement between their corresponding center bolts and nut posts is loosened to thereby present at least a partially new contact surface to said movable contact; said biasing means comprising a first and second concentric helical spring; said first helical spring being wound in a right hand direction; said second helical spring being Wound in a left hand direction; each of said stationary contacts being constructed to comprise a core of A relatively soft current carrying material and a contact surface of relatively hard current carrying material whereby said core of relatively soft current carrying material is effective to absorb shock during contact engagement to I thereby limit contact bounce.

16. A contact structure for mechanical rectifiers; said contact structure comprising a pair of stationary contacts and a guide means and a movable contact; said movable contact being connected to said guide means whereby motion of said movable contact is guided by said guide means; said guide means being positioned and constructed whereby said movable contact is movable into and out of bridging contact engagement with said pair of stationary contacts; each of said pair of stationary contacts being pivotally mounted whereby rotation of each of said pair of stationary contacts about said pivotal mounting presents at least a partially new contact surface for cooperation with the contact surface of said movable contact; the axis of rotation of said pivotally mounted stationary contacts being perpendicular to their contact surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 1,264,685 Rignon Apr. 30, 1918 1,651,414 Settegast Dec. 6, 1927 2,375,416 Huber May 8, 1945 2,458,240 Baskerville Jan. 4, 1949 2,634,343 Rainey Apr. 7, 1953 2,706,759 Williamson Apr. 19, 1955 2,727,114 Kesselring Dec. 13, 1955 

